The present invention relates to a light wood-containing material having an average density in the range from 200 to 600 kg/m3, comprising, based in each case on the wood-containing material:    A) from 30 to 95% by weight of wood particles;    B) from 1 to 25% by weight of a filler having a bulk density in the range from 10 to 150 kg/m3, selected from the group consisting of foamable plastic particles and already foamed plastic particles;    C) from 0.1 to 50% by weight of a binder and, if appropriate,    D) additives,the following relationship being true for the d′ values according to Rosin-Rammler-Sperling-Bennet of the wood particles A) and of the particles of the filler B):d′ of the particles A) ≦2.5×d′ of the particles B).
The present invention furthermore relates to a multilayer wood-base material comprising the wood-containing material according to the invention, a process for the production of light wood-containing materials, a process for the production of a multilayer wood-base material, the use of the light wood-containing material according to the invention and of the multilayer wood-base material according to the invention.
Wood-base materials, in particular multilayer wood-base materials, are an economical and resource-protecting alternative to solid wood and have become very important in particular in furniture construction, in laminate floors and as building materials. Starting materials used are wood particles of different thickness, e.g. woodchips or wood fibers from various timbers. Such wood particles are usually pressed with natural and/or synthetic binders and, if appropriate, with addition of further additives to give board-like or strand-like wood-base materials.
In order to achieve good mechanical properties of the wood-base materials, these are produced with a density of about 650 kg/m3 or more. Wood-base materials of this density or the corresponding parts, such as furniture, are often too heavy for users, in particular private consumers.
The industrial demand for light wood-base materials has therefore increased steadily in recent years, in particular since take-away furniture has grown in popularity. Furthermore, the increasing oil price, which leads to an ongoing increase in, for example, the transport costs, is creating greater interest in light wood-base materials.
In summary, light wood-base materials are very important for the following reasons:
Light wood-base materials lead to simpler handling properties of the products by the end customer, for example on packing, transporting, unpacking or assembly of the furniture.
Light wood-base materials lead to lower transport and packaging costs; furthermore, material costs can be reduced in the production of light wood-base materials.
Light wood-base materials can lead to a lower energy consumption, for example when used in means of transport. Furthermore, for example, material-consumptive decorative parts, such as thicker worktops and side panels in kitchens, which are currently in fashion, can be offered at more favorable cost with the use of light wood-base materials.
Against this background, there is the desire to provide light wood-base materials having, as in the past, good performance characteristics and processing properties.
The prior art contains a wide range of proposals for reducing the density of the wood-base materials.
For example, tubular particle boards and honeycomb boards may be mentioned as light wood-base materials which are obtainable by design measures. Owing to their particular properties, tubular particle boards are used mainly as an inner layer in the production of doors.
A disadvantage of the honeycomb board is, for example, the insufficient screw pull-out resistance, the difficult fastening of fittings and the difficulties in edging.
Furthermore, the prior art contains proposals for reducing the density of the wood-base materials by additions to the glue or to the wood particles.
CH 370229 describes light and at the same time pressure-resistant compression-molded materials which consist of woodchips or fibers, a binder and a porous plastic serving as filler. For the production of the compression-molded materials, the woodchips or fibers are mixed with binder and foamable or partly foamable plastics, and the mixture obtained is pressed at elevated temperature. Binders which may be used are all customary binders suitable for the gluing of wood, such as, for example, urea-formaldehyde resins. Suitable fillers are foamable or ready foamed plastic particles, preferably expandable thermoplastics, such as styrene polymers. The boards described in the examples have a density of from 220 kg/m3 to 430 kg/m3 and a mean flexural strength of from 3.6 N/mm2 to 17.7 N/mm2 at a thickness of from 18 to 21 mm. Transverse tensile strengths are not stated. CH 370229 makes no statement regarding the correlation of the wood particle sizes with the filler particle sizes.
WO 02/38676 describes a process for the production of light products, in which from 5 to 40% by weight of foamable or ready foamed polystyrene having a particle size of less than 1 mm, from 60 to 95% by weight of lignocellulose-containing material and binder are mixed and are pressed at elevated temperature and superatmospheric pressure to give the finished product. The customary binders are mentioned. WO 02/38676 makes no statement regarding the correlation of the wood particle sizes with the filler particle sizes.
JP 06031708 describes light wood-base materials, a mixture of 100 parts by weight of wood particles and from 5 to 30 parts by weight of particles of synthetic resin foam being used for the middle layer of a three-layer particle board, these resin particles having a specific gravity of not more than 0.3 g/cm3 and a compressive strength of at least 30 kg/cm2. Furthermore, it is stated that the specific density of the wood particles should not exceed a value of 0.5 g/cm3. According to JP 06031708, the binders are not subject to any restrictions. JP 06031708 makes no statement regarding the correlation of the wood particle sizes with the filler particle sizes.
In summary, the disadvantage of the prior art is that the light (wood-base) materials described have, for example for furniture production, insufficient mechanical strength, such as, for example, insufficient screw pull-out resistance.
Insufficient mechanical strength can lead, for example, to breaking or tearing of the components. Furthermore, these components tend to additional flaking-off of further wood material on drilling or sawing. In the case of these materials, the fastening of fittings is complicated.
With regard to the combination of good transverse tensile strength with good flexural strength, too, there remains room for improvement in the case of the wood-base materials of the prior art.
The object of the present invention was to provide light wood-containing materials and light wood-base materials which have a lower density compared with the commercially available wood-base materials in combination with good mechanical strengths and good processing properties.
The mechanical strength can be determined, for example, by measuring the transverse tensile strength according to DIN EN 319 or the flexural strength according to DIN EN 310.
Furthermore, these light wood-base materials should preferably be capable of being produced with the use of indigenous, European timbers.
Furthermore, the swelling value of the light wood-base materials should not be adversely affected by the reduced density.